1. Field of the Invention
The present invention relates to a method of manufacturing a print head used in an image forming apparatus, the print head, and an image forming apparatus provided with the print head.
2. Description of the Related Art
For laser printers or copiers, it is known to use a print head adopting an LED array or an organic EL array as a light source, and a rod lens array, as an exposure device. This print head can be sized to be extremely smaller as compared to an exposure device of a system using a semiconductor laser and a polygon scanner. Therefore it is possible to downsize the laser printer or copier.
Incidentally in the print head, one light source in the print head is associated with one dot of an image individually (for example, one-to-one) to perform image formation, but there occur variations in characteristic of each of the light sources, for example, due to manufacturing errors. Then, in the print head, the variations in characteristic of each of the light sources give an adverse influence on each dot in the formed image to generate a longitudinal streak (density unevenness) in the formed image. Therefore, the print head is configured such that each of the light sources is driven by using light quantity correction data (light quantity correction value) to each of the light sources to appropriately adjust the light quantity of each of the light sources, thus preventing the generation of the longitudinal streak.
A method of correcting the light quantity of a light write head is considered as a method of generating the light quantity correction data in such a print head (for example, refer to Japanese Patent Laid-Open No. 2001-270146). According to this light quantity correction method, a third correction coefficient row is found based upon a first correction coefficient row in a case of correcting optical output in such a manner that a diameter of a light spot is uniform and a second correction coefficient row in a case of correcting the optical output in such a manner that optical output of a luminous point is uniform, to make the image density uniform. In consequence, in the print head to which this light quantity correction method is applied, the optical output of each of the light sources is corrected by the found third correction coefficient row, thus making it possible to prevent the variations in image density of the formed image.
In regard to another method of generating the light quantity correction data in the print head, there is disclosed a method of measuring characteristic points (light quantity, luminous diameter, and luminous area) in the luminous intensity to determine light quantity correction data of adjusting the light quantity of each of the light sources, based upon the characteristic points (for example, refer to Japanese Patent Laid-Open No. 11-227254).
Besides, there is disclosed a method of correcting the light quantity of each of the light sources in such a manner that an area exceeding a predetermined threshold from a point of view of the luminous intensity is constant in the print head (for example, refer to Japanese Patent Laid-Open No. 2002-370401).
Besides, there is disclosed a method of correcting the light quantity of each of the light sources in such a manner that the light amount exceeding a predetermined threshold in a beam profile of each of the light sources is constant in the print head (for example, refer to Japanese Patent Laid-Open No. 11-342650).
Besides, there is disclosed a method of producing light quantity correction data to adjust the light quantity of each of the light sources in such a manner that a cross-sectional area in any luminous intensity in a beam profile of each of the light sources is within a desired distribution in the print head (for example, refer to Japanese Patent Laid-Open No. 2001-322310).
In this manner, according to the conventional print head, each of the light sources is driven by using the light quantity correction data produced in such a manner that the light quantity, the luminous diameter or the luminous area in each of the light sources becomes a constant value or approaches the constant value.
The conventional print head, however, can suppress the generation of the longitudinal streak in the formed image, and cannot sufficiently prevent the generation of the longitudinal streak. Therefore the print head that drives each of the light sources by using the above-mentioned light quantity correction data has room for improvement from a point of view of appropriately preventing the generation of the longitudinal streak.